On the microenvironments surrounding dansyl sequestered within class I andII xerogels

We report on the static and time-resolved fluorescence spectroscopy of dans yl sequestered within two xerogels that were formed from tetraethylorthosil ane (TEOS) mixed with ppm levels of dansylamide or dansyltriethoxysilane. T hese are referred to as class I and II xerogels, respectively. Experiments were performed on these samples as they progressed from liquids to xerogels over a period of 1 year. The results show that the average local microenvi ronment surrounding the dansyl dopant is different in the class I and II xe rogels. Specifically, even though the dipolarity surrounding the dansyl dop ant increases as both samples progress from liquids to xerogels, the local dansyl microenvironment within a class II xerogel is always more heterogene ous in comparison to the class I xerogel. In an aged xerogel, the local dip olarity surrounding the dansyl dopant is greater for the class I xerogel th an for the class II xerogel. These results are discussed in terms of a mode l that has the dansyl locating preferentially within Si-OH- and SiO2-rich r egions for the class I and II xerogels, respectively.